How does explanation of zebra striping stand up to studies of prey preference in spotted hyena and lion?

(writing in progress)

See
https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.473.2911&rep=rep1&type=pdf
https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.2006.00183.x
https://zslpublications.onlinelibrary.wiley.com/doi/10.1017/S0952836905007508#:~:text=The%20most%20preferred%20weight%20of,weight%20range%20are%20generally%20avoided.
https://www.academia.edu/1961984/Prey_preferences_of_the_lion_Panthera_leo_

I have previously explained the striping in the plains zebra according to limitations in the visual system of its main predators, particulaly the spotted hyena (see https://www.inaturalist.org/journal/milewski/67289-the-adaptive-function-of-striping-in-the-plains-zebra#).

How does this explanation stand up to our knowledge of the actual pre preferences of the spotted hyena and the lion?

First, here is a reminder of the gist of my explanation.
 
1) Zebras are plains game and camouflage colouration has never been demonstrated in any species of plains game; on the contrary many species of plains game (other than zebras) are conspicuous and accentuate this conspicuousness by individual displays of fitness to approaching predators.
 
2) Zebras and non-striped species in the same genus (Equus) relate differently to other plains game because a) like-size ruminants are more abundant than Equus only in the habitats of zebras, b) zebras are attracted to other plains game whereas other species of Equus are not; and c) zebras differ from the coexisting ruminants, as well as the Asiatic wild ass (Equus spp.) in refraining from anti-predator displays of individual fitness.
 
3) The main predator against which whole-body colouration is likely to have evolved in all species of Equus (including unstriped species in Eurasia) is the spotted hyena (Crocuta crocuta), a species which uses combined speed and endurance and thus depends on first carefully scanning the groups for the most vulnerable individual – whether by day or by night – as distinguished not by its shape but by the finest subtleties of its pattern of movement. And the eyes of the spotted hyena are more specialised for scanning than those of other large predators in zebra habitat, such as felids and the painted hunting dog (Lycaon pictus).
 
4) Zebras breed and grow more slowly than other plains game of similar body size; they risk demographic liability because the predatory pressure on them is determined not by their own productivity but the productivity of the prevailing ruminants with which they coexist. Hence their survival depends on anti-predator tactics additional to cursoriality, precociality, thick skin, and fighting back in self-defence, and foiling the scanning by the spotted hyena would serve this purpose by deflecting the predator’s attention on to adjacent prey such as wildebeests (Connochaetes).
 
5) Zebra striping produces a flicker-effect to the human eye and is therefore likely to present a far greater flicker-effect to the eye of the spotted hyena, which are particularly sensitive to motion. This is likely to retard detection of the most vulnerable individual in the group, particularly because a) it is precisely the small-scale movements that the spotted hyena needs to discern, b) the different scales of striping on e.g. legs vs body mean that flickering would occur on different parts of the zebra depending on distance and illumination (night, day, or twilight), and c) the evolutionary ability of the spotted hyena to counter such retinal disruption is limited by its need to remain as efficient as possible in scanning its long-term mainstay of ruminant prey.

In 'Prey preferences of the lion', Hayward found zebra are preyed upon at numbers greater than their abundance in the general population by lions.

I think there may be a catch here. In most national parks the ecosystem has rather artificially been centred on water, often artificially provided. This has modified what were originally long-range migratory systems in such a way that the population of the lion has increased, sometimes to the detriment of the lion’s bitter enemy, the spotted hyena, which the lion will kill out of hand any time it can. So the original predatory regime may have been distorted somewhat in favour of the lion and in disfavour of the spotted hyena. (As an interesting aside, an important fact about the spotted hyena is that it resembles equids in having far slower reproduction than that of felids and canids, which explains why it is often slow to recolonise areas from which it has been exterminated by poisoning, whereas the felids and canids rapidly recolonise.) This would still not explain the obvious question ‘but how do the zebras survive if they are predated to intensely by the lion?’ Part of the answer may be a certain longer-term cycle of drought and good times. When droughts occur in African national parks, the zebras are likely to provide a greater-than-average proportion of the diet of the lion, for several reasons. Firstly, at such times animals must drink and their vulnerability around water increases. Secondly, zebras are unlike coexisting ruminants in surviving poverty better, and so zebras seldom die from drought, becoming temporarily a larger part of the whole ungulate community. So in a national park provided with artificial water-points as an approximate substitute for the original long-range migrations, a situation can arise where and when, at least during drought, the zebras can be predated beyond their capacity to replace losses by breeding. But zebras are long-lived, and once conditions swing the other way the zebras are partly freed of the losses of predation by the lion and can recover their numbers. Another way of putting this is that ruminants, such as the wildebeest, tend to be ‘limited’ mainly by mishap, whereas zebras tend to be limited mainly by predation. It is well-known that in the case of the Serengeti migrations most dead wildebeest die from mishap, not predation, and this includes not only drought-induced mortality but also just physical accidents while migrating, e.g. lame legs. This is why, surprisingly enough, the main vultures in the Serengeti, which eat many wildebeests, tend to reach the carcasses before they are reached by any mammalian scavenger. In both cases, i.e. spotted hyena and Gyps vultures, the main food in migratory systems if fresh meat, not carrion scavenged; the difference is that the spotted hyena is also capable of killing in its own right, whereas the vultures are not, depending instead on mishaps.
 
If the same were true for hyenas, we would expect zebras to be in real trouble (and their numbers are in decline) but in 'Prey preferences of the spotted hyena etc' he finds that zebra are not a big prey item for the hyena (he says actively avoided but that terminology seems too strong).

I mentioned earlier that although the painted hunting dog poses a real threat to zebras it can usually be seen to be rebuffed. A similar principle applies to zebras: zebras will stand their ground near the spotted hyena in a way it will not near the lion. It is not that the spotted hyena actively avoids the zebras, it is that much of the time the defences of the zebras are so great that all predators (including to some degree the lion, as shown by the frequency of scars on the rump) fail when they hunt zebras. It is not that painted hunting dog and spotted hyena do not ‘prefer’ zebras; they would kill them frequently if they could. It is not that they ‘avoid’ zebras; it is that they often try to hunt them (even if merely by sussing out the group for vulnerable individuals) but usually fail. So the above analysis of ‘prey preferences of the spotted hyena’ risks being a bit misleading in the case of zebras: the figures measure not so much ‘preference’ on this case but rather ‘success’. In Hans Kruuk’s pioneering studies of the spotted hyena in the ‘seventies, he noticed that the spotted hyena adopted special methods with the plains zebra. Whereas the usual approach was that one individual hyena would chase an ungulate and kill it, being immediately joined by many other individuals to finish off the carcase, when the predator set out to hunt the plains zebra there was group-level preparation, in which the individuals of the spotted hyena went through certain rituals as if planning the event. Even then, there is no real collaboration because it is ‘every hyena for itself’, but the hunt then winds up being gregarious right from the start, with many individuals, all in it for themselves, all hunting the quarry zebra individual simultaneously. The quarry individual zebra is usually chosen by a dominant female hyena, and the mob all try to exploit her expertise for their own selfish gain. But the point is that in the case of both painted hunting dog and spotted hyena, the success of hunting the plains zebra is limited unless cultural and social factors are ramped up for the occasion. In the case of the painted hunting dog in the Serengeti ecosystem, the only real success in hunting the plains zebra was in those groups in which at least one member had mastered a certain culturally inherited knack of catching the zebra by the upper lip to immobilise it safely. In the case of the spotted hyena, various individuals in the clan could initiate a chase of zebras but two things tend to apply: a) the usual initiator is a particularly strong/experienced/confident individual, i.e. both female and socially dominant, and b) there needs to be a bit of a ‘rabble-rousing’ ceremony in which, effectively, the hyena individuals say to each other ‘you buggers are going to lose out big-time because I’m going to be the one to steal the zebra’. Although the intentions are selfish in this way, the result willy-nilly is gregarious chasing, which is what it usually takes to bring the zebra down.

Why should they avoid zebra more than other species? Sure zebras fight back more, but can that be it (it doesn't stop the lion?
 
Well, it does often stop the lion because, as you can see from the remarkable frequency of surviving individual zebras with scarred rumps, the lion often fails; and in many or most cases of the lion scratching the rump in vain it was the case that the lion was dislodged by a backward kick, with both legs simultaneously, by the attacked zebra.
 
Or can it be that zebra makes it hard for C. crocuta precisely because of the way their canid vision operates compared to the felid eye?

The field studies seem to indicate that both factors apply to the spotted hyena in its quest for zebras as prey. Firstly, it relatively seldom actually embarks on a full-out chase of zebras, although often ‘testing’ the group by alarming it to see how it reacts; and secondly the spotted hyena only really stands a good chance of catching and killing any zebra chased if it has numbers on its side. Of course, Kruuk’s observations were made by day, so we need more information on how the spotted hyena hunts zebras at night.
 
I think this likely lends support more than anything.

(writing in progress)

Posted on 08 de setembro de 2022, 04:47 AM by milewski